Applicant's prior U.S. Pat. No. 4,171,206 describes a pressure swing adsorption (PSA) process (hereinafter the "base cycle") which can be used for the fractionation of a multicomponent gas mixture composed of (1) a bulk primary component, (2) a bulk secondary component more strongly sorbed than the primary component and (3) a minor quantity of one or more dilute components less strongly sorbed than the secondary component. By way of example, the '206 patent applied the base cycle to the production and recovery of pure hydrogen (primary component) and CO.sub.2 (secondary component) from the gaseous effluent of a shift converter in a hydrocarbon reforming plant where the minor quantity of dilute components consisted of CH.sub.4 and CO.
The present invention provides an improvement to the base cycle whereby the recovery of the primary component is significantly increased.